|Two soybean aphid eggs laid next to the bud scales of buckthorn.|
Photo by Marlin E. Rice, Iowa State Extension.
As the days get shorter and cooler in the fall,insects enter into an inactive state of arrested development called diapause. During the winter an insect’s metabolic rate drops to one-tenth or less, so it can use stored body fat to survive. Many insects also produce alcohols that act like antifreeze. These insects’ bodies can reach below-freezing temperatures without forming cell-damaging ice crystals. In the spring, as temperatures rise, diapause is terminated and insect growth and development return to normal.
Even with all of these adaptations, extreme cold and temperature fluctuations can indeed affect insect survival depending on how low the temperature dropped, how long the cold persisted, and if snow cover was present. Other factors to consider are microclimates and how protected insects are in their hiding places. So where do insects hide during the winter?
Insects spend winter in various life stages. Aphids overwinter as eggs laid in the bud scales of woody plants. Bagworm eggs are safely tucked away inside a bag. Tent caterpillar eggs can be found in a mass on branches. Bean leaf beetles spend winter as adults under loose bark or fallen leaves. Lady bugs congregate under firewood. Japanese beetle grubs hide deep in the soil, and some butterflies overwinter as pupae in a cocoon or chrysalis. Each insect has its own way of dealing with cold weather. As much as we would like to think that a rough winter will take care of those pesky insects, most will survive.